Many investigators have attempted to provide fire protection for cable trays. U.S. Pat. No. 4,194,521 relates to a corruguated structure coated with an intumescent material, said structure being used as a tray for supporting insulated electrical cables. This structure is located beneath the cables and will only provide fire protection if the fire starts below the assembly. No fire protection is provided for the sides or top of the cable tray.
Another attempt to provide more fire protection for cables is shown in U.S. Pat. No. 4,276,332 which relates to a fireproof cable tray which completely surrounds the cables. The major disadvantages of this system are its inability to fit around an existing metal cable tray since it is designed to function as the cable tray and, most importantly, its inability to dissipate the heat build-up from resistance loss as power runs through the cables. The predominant reason for supporting cables in trays suspended above the floor is to allow air flow around them for cooling. However, if the tray itself is surrounded by inorganic fiber insulation, heat from the cable will not be dissipated to the surroundings and the cables must be derated. This heat build-up, if allowed to remain unchecked, could also cause a cable tray fire.
U.S. Pat. No. 4,064,359 discloses insulation materials for protecting electrical cables, cable trays or conduits from fire. However, the inherent disadvantage of cable temperature build-up under normal operating conditions still remains a serious problem.
U.S. Pat. No. 4,069,075 relates to intumescent coating materials for structural members and particularly a wire mesh attached to a structural member with a self-adhering char-forming intumescent coating applied thereover and to the structural member.